In recent years, there have been attempts to provide strength testing devices for dynamic testing. Some of these devices would involve developing isokinetic exercise apparatus of which the user moves at a constant velocity regardless of the amount of resistance that is applied. The isokinetic exercise allows the user to move throughout an entire range of motion safely, because the force offered by the apparatus is accommodating to the user force.
Conceptionally, isokinetic exercise is similar to pushing against an air pump piston. If a user could regulate the amount of air exiting the pump, then when the user pushes hard on the air pump, there would be a great amount of back pressure and thus the person would encounter a great amount of resistance. If the user pushes only slightly on the air pump, then the user would encounter only a slight amount of resistance. Whether the user pushes hard or slow against the piston, the piston moves at a substantially constant speed, and thus the accommodating concept of isokinetics. Such devices are shown in U.S. No. 4,041,760 of Henson et al, U.S. Pat. No. 3,896,62 of Henson et al, and U.S. Pat. No. 3,465,592 of Perrine.
Another advantage of the isokinetic mode is that it allows a clinician with no prior familiarity with the patient's strength capabilities to test the patient by simply placing him or her in an isokinetic mode. The clinician can safely ascertain the patient's strength capabilities. A disadvantage and criticism of the isokinetic mode is, however, that it does not simulate normal movement. A person does not normally move at a constant velocity. In normal lifting, a person accelerates at the beginning of the lifting stroke and decelerates toward the end of the stroke. For this reason, there have been inventions that have addressed the need to operate in an isotonic (constant force) mode. For example, U.S. Pat. No. 3,902,480 of Wilson has provided an electrical-mechanical isotonic or isokinetic exercise system. U.S. Pat. No. 4,184,678 of Flavell et al shows a programmable acceleration exerciser. In this apparatus, Flavell has provided means for the user to choose among a variety of preselected acceleration and constant velocity patterns. U.S. Pat. No. 4,138,106 of Bradley shows a weight training apparatus in which the force varies according to the initial acceleration. The user is not, however, able to choose a preselected force and accelerate freely in either Flavell or Bradley systems. U.S. Pat. No. 4,544,154 has provided a programmable isokinetic or isotonic system with a feedback loop using hydraulic components. Once the user chooses a preselected force at the beginning of the test, the feedback loop maintains that force regardless of the varying velocities.
Although strength measurements are needed in any lifting analysis, the use of a strength testing apparatus alone will not provide the clinician with the information needed in determining a "ready for work" status. The technique of lifting is one of the fundamental determinates to predicting back injury resulting from lifting.
There have been devices which measure joint ranges of motion. U.S. Pat. No. 3,929,335 of Malick was developed for the use of motivating a patient in need of occupational therapy to exercise. It includes his movement and exercise of muscles after a long period of disuse for nerve damage. The exercises are often difficult and the patient must, in many cases, be constantly reminded to continue the exercise.
U.S. Pat. No. 4,108,164 of Hall relates to measuring the range of motion in the back with various activities. It includes a jacket containing clinometers. The sensors are attached to a jacket instead of to the subject. Using this approach, there would be slippage between the jacket and the subject. The degree of slippage depends on how closely the jacket approximates each individual. In addition, in the process of lifting, the concern is not necessarily with the spinal technique but, rather, in the hip and knee synchronization in general. As an example, during the lifting process, it is important that the knees are flexed substantially enough to allow the user's back to remain near perpendicular to the floor in order to decrease the force on the user's back.